Extrinsic-intrinsic crossover of the spin Hall effect induced by alloying

We report the observation of the crossover between the extrinsic and intrinsic spin Hall effect induced by alloying. We found that the spin Hall angle, the ratio of the spin Hall conductivity to the electric conductivity, changes drastically by tuning the composition of the Au-Cu alloy. The spin Hall angle changes sign only in a limited range of the Cu concentration due to the extrinsic skew scattering, while the intrinsic contribution becomes dominant with increasing Cu concentration. This observation provides essential information for a fundamental understanding of spin-orbit physics.